zone-yield.js

var contents = yield fs.readFile('bla');

yield zone.create(() => {
  http.get('google.com/bla').pipe(fs.createWriteStream('cache/file1'))
  http.get('google.com/bl2').pipe(fs.createWriteStream('cache/file2'))
  http.get('google.com/bl3').pipe(fs.createWriteStream('cache/file3'))
});

console.log('all done!')

Well, I think this came up earlier, but generators (yield) support is not implemented yet for zones.
The error you're seeing is caused by the fact that generator support for node needs to be turned on with a flag, try:

node --harmony zone-yield.js

That still won't do anything useful but it turns on generator support.